SOME IMPORTANT TREE INSECTS 
A. G. RUGGLES. 
During the last year, there have been many calls made upon 
the division for advice concerning tree insects. In all, about two 
hundred letters have been answered on this subject alone, besides 
the many telephone calls for aid. The relative importance of these 
insects is shown by the order in which the insects are mentioned 
below: 
Bark borers, canker worms, cottony maple scale, spiny elm 
caterpillar, walnut Datana, yellow striped oak worm, scale in- 
SECES, EEC: 
The injury done by the borers to the several species of oaks 
has been the subject of most inquiry. The insect causing this 
damage to the oak timber, called the two-lined chestnut borer 
(Agrilus bilineatus), has been the object of close investigation 
this past summer and a number of new points have been brought 
out in its life history that may enable us to later find a better 
method of control. 
For this locality in a normal year, the life cycle has been 
definitely determined as follows: The adult beetles fly from June 
15th to July 15th, during which period the eggs are laid. The 
beetles are most numerous around July Ist. The eggs are laid 
singly or in batches of three to ten in the bottom of natural 
crevices in the bark. In ten days or more, these hatch and imme- 
diately bore into the bark until they reach the wood. After 
they burrow their length in the wood, they return to the growing 
layers between the wood and the bark, called the cambium, where 
all the injurious burrows are made. During the early stages of the 
grub life, the burrows are made with the grain of the wood or 
in an oblique direction. lL.ater, particularly in the last stage, the 
burrow is almost always across the grain of the wood. It is at 
this time that the tree is being actually girdled. If the burrows 
extend far enough or if the grubs are numerous enough, the tree 
then dies. 
In August the majority of the grubs have made their pupal 
chambers in the bark. In the spring, about June 10th, they 
pupate and adults are seen at the time mentioned before. 
